The art of forming shaped articles from particulate mixtures is well known in the art. Classically, a desired particulate material is mixed with a binder and then formed into the desired shape, this being called a green body. The green body is then fired to provide a fusion of the particulate material and to drive off the binder, thereby producing the desired shaped product with proper surface texture, strength, etc.
In the production of shaped objects in the manner above described, it has been found that the binder is a necessary evil. It must be used in order to form an object of practical use, but it also must be removed before the part can be sintered.
The prior art has recognized this problem and has therefore attempted to remove binder from the shaped green body prior to the step of firing. Examples of such prior art are shown in the patent to Strivens U.S. Pat. No. 2,939,199 as well as in British patent No. 808,583. While systems using the procedures described in the above noted patents can provide advantages over prior art procedures wherein removal of the binder prior to firing was not utilized, articles formed in accordance with the teachings of these prior art patents still have the tendency to crack during the binder removal as well as during the firing operation. The reason for this is that the binder is removed from the green body by means of a solvent when the binder is in the solid state. It is known that when the binder and the solvent are mixed together, the binder-solvent mixture has a tendency to expand. Since the binder is in the solid state, it can not readily move within the green body and the expansion within the green body can become greater than the van der Waals forces holding the particulate material together. This will cause the cracking which is then further accentuated in the final firing step if the article is even capable of somewhat retaining its shape.